The human nervous system senses current information and conditions, which it then sends to various muscles to respond. As one example, consider the facial and neck nerves. These motor nerves control the muscles of facial expression and, thus, an individual's outward manifestations of well being and emotion. Neuromuscular defects can disrupt this information exchange and lead to undesired muscle responses.
The involuntary contraction of facial or neck muscles (also known as dystonias) can distort an individual's facial expressions and garble the outward appearance of the individual's feeling of well being and emotional state. For example, one type of dystonia, called belpharospasm, creates uncontrolled blinking and spasms in the eyelids. Another form of dystonia causes uncontrolled grimacing. Dystonias can also affect neck muscles. For example, one form of dystonia, called torticollis, causes uncontrolled contraction of the neck muscles.
Apart from these hyperfunctional disorders, normal contraction of facial and neck muscles (e.g., by frowning or squinting) can form permanent furrows or bands in the skin over time. These furrows or bands can present an aesthetically displeasing cosmetic appearance, and exposure to the sun can accelerate this undesired wrinkling process. As a more specific example, the facial muscle corrugator supercilii draws the eyebrows downward and inward, producing vertical wrinkles of the forehead (also called glabellar frown lines). For this reason, the corrugator supercilii is known as the frowning muscle and has been called the principal agent in the expression of suffering. Dystonias affecting the corrugator supercilii can lead to an unfortunate, continuous frowning expression, as well as the formation of hyperfunctional frown lines and wrinkles in the face.
A surgical forehead lift procedure is one therapeutic modality often used to remove glabellar frown lines. The forehead lift requires a large incision that extends from ear to ear over the top of the forehead. This surgically invasive procedure imposes the risk of bleeding and creates a large skin flap that reduces blood supply to the skin. Numbness of sensory nerves in the face, such as the supraorbital nerve can also result.
A less invasive therapeutic modality is the administration of invertebrate exotoxins. For example, injection of the serotype A of the Botulinum toxin produces a flaccid paralysis of the corrugator supercilii. Tests have demonstrated that Botulinum toxin A may be administered into the musculature of the face without toxic effect to produce localized muscle relaxation for a period of about six months. The desired removal of hyperfunctional frowning lines is temporary, and repeated treatments are needed about every 3 to 6 months.
Another form of treatment, disclosed in U.S. Pat. No. 5,370,642 to Keller, uses laser energy to eliminate glabellar frown lines and forehead wrinkles. The laser energy is used to resect large sections of the corrugator supercilii (as well as other facial muscles) and thereby inactivate the muscles. Like the surgical forehead lift, numbness of the supraorbital nerve and other sensory nerves in the face can result.